Billionaire hedge funder Carl Icahn disclosed a large stake in Apple today and said he was encouraging the company to increase the buyback program — on Twitter, of all places.

Those two tweets alone, however, sent Apple shares up about 5% and added about $17 billion to Apple's market cap. The jump in price comes at a time when Apple is facing an issue with its public image — and whether the creator of the iPhone can still innovate.

So, how much more valuable is Carl Icahn's twitter activity compared to certain companies?